FDA releases Guidance Document for Nitinol Devices
In July 2021, the FDA released its final version of a Guidance Document titled “Technical Considerations for Non-Clinical Assessment of Medical Devices Containing Nitinol.” This guidance provides clear expectations from the Agency with respect to benchtop testing of medical devices which incorporate nitinol features. A few key points of consideration are highlighted below:
Superelasticity vs. Shape Memory Behavior
Depending on the application and intended use, nitinol can be “tuned” via composition and thermal treatments to either behave as a superelastic material or to exhibit shape memory behavior. The two behaviors are different, and the FDA expects the submission to clarify which one is being used.
2. Fatigue loading test conditions
The FDA states:
Some devices are exposed to cyclic loading conditions during use (i.e., fatigue loading). If you conduct fatigue tests, we recommend that you use a clinically relevant liquid test solution (e.g., phosphate buffered saline (PBS)). Since fatigue testing of nitinol in air has been shown to be sensitive to test frequency due to heating effects, we do not recommend that you conduct fatigue tests of nitinol in air. If you conduct fatigue testing of nitinol in air, we recommend that you provide a scientific justification for the test environment used.
3. Nickel Release: Biocompatibility, Labeling - Warnings
Biocompatibility guidance is offered as it relates to in-vitro nickel release testing, which should be performed to compare against a Tolerable Intake (TI) value for nickel which can be found in ISO 10993-17:2012 “Biological Evaluation of medical devices— Part 17: Establishment of allowable limits for leachable substances.” In consideration for patients who may have an allergic reaction to nickel, the FDA recommends the following warning be included for permanent contacting devices:
Warning: This device contains nitinol, an alloy of nickel and titanium. Persons with allergic reactions to these metals may suffer an allergic reaction to this implant. Prior to implantation, patients should be counseled on the materials contained in the device, as well as potential for allergy/hypersensitivity to these materials.
The full guidance document can be downloaded here.
